The term myosin is now used to refer to a diverse superfamily of molecular motors, capable either of translocating actin filaments or of translocating other cargo along fixed actin filaments. This superfamily is currently represented by at least 11 distinct classes based on sequence homology. All types of myosins that have been purified are multimeric and possess three major functional domains, a head, a neck and a tail. The head appears to be largely conserved among the different subgroups of the family. It contains the basic structural elements which are the actin- and the nucleotide-binding sites. The neck consists of a long single alpha-helical strand which is stabilized by the binding of light chain subunits or calmodulin. The tail, or anchor domain, is the most diverse in its primary sequence and structure and its function is subject to the greatest speculation in the novel classes of myosin. We are particularly interested in two of these myosins: myosin V which has been shown to be present in mammals and yeast and may be implicated in membrane trafficking or targeting and myosin X, a recently cloned myosin of unknown characteristics and function. We are attempting to purify the myosin V from chicken brains and clone it and the myosin X from Drosophila melanogaster.